FALL OF COROLLA 403 



withering sets in. The separate petals fall from the poppy, 

 the rose, the rock-rose, the crane's-bill, and the flax ; in 

 the pimpernel, the comfrey, and the sage the gamopetalous 

 corolla falls as a whole ; in the daffodil, the dandelion, and 

 the honeysuckle withering precedes the fall. It is well 

 known that some flowers last only a single day, or even a 

 few hours, and that withering sets in regularly whether 

 polHnation'has occurred or not. Fitting (1909, a and b) states 

 that in the orchid Phalcenopsis violacea the corolla, which 

 would otherwise remain fresh for a month, withers a day or 

 two after pollination has taken place, while in Geranium 

 pyrenaicum and Erodium Manescavi the petals fall about 

 an hour after pollination. In these cases the stimulus is 

 connected with pollination, for fertilisation cannot have 

 taken place. The fall may be brought about in the case of 

 the orchid by the application of dead pollen or of pollen of 

 other plants. When the petals fall fresh there is a preformed 

 abscission layer, as in leaves. The male flowers of many 

 dicUnous species fall as a whole, e.g. Begonia, Mercurialis, 

 Populus (inflorescence). Abscission of female flowers may 

 take place if pollination fails, as in the scarlet runner or 

 the potato. Abscission of flower buds in unfavourable 

 conditions, as when poisoned by coal-gas or dried up, is not 

 infrequent. Abscission, whether of flowers or of inflor- 

 escences, may be regarded as the unloading of an organ 

 which, while present, draws on the supply of water and food 

 substances, and which has become useless, either as having 

 performed its functions, or as having failed in the normal 

 span to do so. The rapid withering of petals which do not 

 fall suggests that changes in the water relations may be an 

 important cause. 



Post-floral Movements. — Another class of post-floral 

 changes are those which result in specific movements, 

 particularly of the peduncle. The most remarkable case is 

 that of Arachis hypogcea, the earth-nut. The floral axis, 

 between the calyx and the ovary, elongates very greatly, 

 reaching a length of as much as five inches, and growing 

 downwards so that the young fruit, which meanwhile 



